wankunde opened a new pull request, #41676:
URL: https://github.com/apache/spark/pull/41676
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### What changes were proposed in this pull request?
DAGScheduler will get the preferred locations for each RDD partition and try
to allocate the task on the preferred locations.
We can remove the duplicate preferred locations to save memory.
For example. reduce 0 needs to fetch map0 output and map1 output in host-A,
then the preferred locations can be Array("host-A").
### Why are the changes needed?
To save driver memory for large job, too many preferred locations may cause
OOM.
```
2023-06-19T14:14:18.501-0700: [Full GC (Allocation Failure)
2023-06-19T14:14:18.501-0700: [Class Histogram (before full gc):
num #instances #bytes class name
----------------------------------------------
1: 2980686820 95381978240 scala.collection.immutable.$colon$colon
2: 2978345818 71480299632
org.apache.spark.scheduler.HostTaskLocation
3: 24388384 3963604560 [C
4: 24265128 776484096 java.lang.String
5: 368944 560810384 [Ljava.lang.Object;
6: 2927846 421609824 java.net.URI
7: 16239585 389750040 java.lang.Integer
8: 2540273 243866208 org.apache.hadoop.fs.FileStatus
9: 676141 203208736 [B
10: 3845164 184567872 java.util.Hashtable$Entry
11: 3174033 152353584
java.util.concurrent.ConcurrentHashMap$Node
```
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Added UT
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